Batteries as principal or back-up power sources have numerous applications in such industries as computer technology and telecommunications. In these applications it is important that the battery be maintained at a fully charged condition in order to function properly.
One particular application for batteries is as an emergency power source for telecommunication equipment located outdoors. If the regular power supplied by an a.c. source fails, the battery must be able to provide the necessary voltage until such time as the a.c. power is restored. It is common in such applications that a battery charger be connected across the batteries such that they are constantly maintained at the proper voltage levels.
It is known that the resistance of batteries varies as a function of ambient temperature conditions such that charging levels, if kept constant, would either provide insufficient or excessive charging or float voltage. This can result either in an under-charged battery if a low float voltage is provided, or possibly a damaged battery if excessive voltage is applied. It is therefore a requirement to control the float voltage in response to changes in ambient temperature.